Method and device for distributing idle user equipment in multi-carrier based mobile communication system

ABSTRACT

The present invention relates to a method and device for distributing idle UE by a carrier in eNB of a multi-carrier based mobile communication system. The method of distributing idle UE in a multi-carrier based mobile communication system according to the present invention includes a process of determining a search rate by a carrier on the basis of information representing load on the carrier, a step of determining a cell reselection priority on the idle UE on the basis of the determined search rate, and a process of transmitting the determined cell reselection priority to the idle UE.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/286,250,filed Feb. 26, 2019, which is a continuation of application Ser. No.15/144,634, filed May 2, 2016, now U.S. Pat. No. 10/237,800, which is acontinuation of application Ser. No. 14/358,711, now U.S. Pat. No.9,332,470, which is the National Stage of International ApplicationPCT/KR2012/009690, filed Nov. 15, 2012, which claims priority to KoreanApplication No. 10-2011-0118891, filed Nov. 15, 2011, the disclosures ofwhich are herein incorporated by reference.

BACKGROUND 1. Field

The present disclosure relates to a mobile communication system, andmore particularly, to a method and a device in which an evolved node B(eNB) of a multi-carrier based mobile communication system distributes auser equipment (UE) in an idle mode (hereinafter, referred to as ‘idleUE’) by a carrier.

2. Description of Related Art

In a conventional 3GPP (3rd Generation Partnership Project) system, aneNB has one carrier for each cell, and a UE accesses the one carrier toreceive a service. In the conventional 3GPP system, a cell selectionprocess and an RRC (Radio Resource Control) connection setting processof the UE are as follows.

In initial start or a change in a radio environment, the UE searches forthe most suitable cell through a cell selection/reselection process,receives system information from an eNB of the searched cell, and campson the searched cell. Then, when a call is started or a paging processis performed in a network, the UE sets an RRC connection through arandom access process.

In the conventional art, an operation for dynamically changing prioritybased on load by a carrier has not been performed for a UE, RRCconnections of which are released, based on load by a carrier. It isnecessary to provide a method for efficiently distributing a UE, RRCconnections of which are released, on the basis of informationrepresenting load on each carrier that is used in a multi-carrier based3GPP LTE system.

SUMMARY

The disclosure has been made to solve the above-mentioned problem in theprior art, and an aspect of the present disclosure is to provide amethod and a device for efficiently distributing a UE in a multi-carrierbased mobile communication system.

Another aspect of the present disclosure is to provide a method and adevice for distributing a UE on the basis of information representingload on each carrier that is used in a mobile communication system.

In accordance with an aspect of the present disclosure, a method fordistributing an idle user equipment in a multi-carrier based mobilecommunication system includes the steps of: determining a search rate bya carrier on a basis of information representing load on a carrier;determining cell reselection priority for the idle user equipment on abasis of the determined search rate; and transmitting the determinedcell reselection priority to the idle user equipment.

In accordance with an aspect of the present disclosure, a method fordistributing an idle user equipment in a multi-carrier based mobilecommunication system includes the steps of: determining a cellreselection search rate by a carrier on a basis of informationrepresenting a predetermined number of cell load averages by a carrier;determining cell reselection priority for the idle user equipment on abasis of the determined search rate; and transmitting informationrepresenting the determined cell reselection priority to the idle userequipment.

In accordance with an aspect of the present disclosure, a method fordistributing an idle user equipment in a multi-carrier based mobilecommunication system includes the steps of: determining a cellreselection search rate by a carrier on a basis of informationrepresenting distribution of active user equipments; determining cellreselection priority for the idle user equipment on a basis of thedetermined search rate; and transmitting information representing thedetermined cell reselection priority to the idle user equipment.

In accordance with an aspect of the present disclosure, an apparatus fordistributing an idle user equipment in a multi-carrier based mobilecommunication system includes: a control unit that determines a searchrate by a carrier on a basis of information representing load on acarrier, and determines cell reselection priority for the idle userequipment on a basis of the determined search rate; and a transmissionunit that transmits the determined cell reselection priority to the idleuser equipment.

In accordance with an aspect of the present disclosure, an apparatus fordistributing an idle user equipment in a multi-carrier based mobilecommunication system includes: a control unit that determines a cellreselection search rate by a carrier on a basis of informationrepresenting a predetermined number of cell load averages by a carrier,and determines cell reselection priority for the idle user equipment ona basis of the determined search rate; and a transmission unit thattransmits information representing the determined cell reselectionpriority to the idle user equipment.

In accordance with an aspect of the present disclosure, an apparatus fordistributing an idle user equipment in a multi-carrier based mobilecommunication system includes: a control unit that determines a cellreselection search rate by a carrier on a basis of informationrepresenting distribution of active user equipments, and determines cellreselection priority for the idle user equipment on a basis of thedetermined search rate; and a transmission unit that transmitsinformation representing the determined cell reselection priority to theidle user equipment.

According to the embodiments of the aforementioned present disclosure,it is possible to distribute a UE on the basis of carrier distributionand an active UE. Furthermore, it is possible to adjust load betweencarriers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a mobile communication system to whichthe present disclosure is applied;

FIG. 2 is a flowchart illustrating a method for distributing an idle UEby a carrier in a mobile communication system according to a secondembodiment of the present disclosure;

FIG. 3 is a flowchart illustrating a method for distributing an idle UEby a carrier in a mobile communication system according to a thirdembodiment of the present disclosure;

FIG. 4 is a flowchart illustrating a method for distributing an idle UEby a carrier in a mobile communication system according to a fourthembodiment of the present disclosure;

FIG. 5 is a flowchart illustrating a method for distributing an idle UEby a carrier in a mobile communication system according to a fifthembodiment of the present disclosure;

FIG. 6 is a block diagram schematically illustrating a configuration ofan eNB 103 according to an embodiment of the present disclosure;

FIG. 7 is a flowchart illustrating a method in which an eNB 103according to an embodiment of the present disclosure distributes an idleUE; and

FIG. 8 is a flowchart illustrating a method for distributing an idle UEby a carrier in a mobile communication system according to a sixthembodiment of the present disclosure.

DETAILED DESCRIPTION

In the following description of embodiments of the present disclosure, adetailed description of known functions or configurations incorporatedherein will be omitted when it is determined that the detaileddescription thereof may unnecessarily obscure the subject matter of thepresent disclosure. Hereinafter, embodiments of the present disclosurewill be described with reference to the accompanying drawings.

A multi-carrier mobile communication system according to embodiments ofthe present disclosure includes an eNB and a UE capable of using atleast two carriers. Particularly, in a call connection, the UE isconfigured to use at least one carrier that is provided by the eNBaccording to UE information. Consequently, in the mobile communicationsystem according to the embodiments of the present disclosure, it ispossible to reduce a connection attempt rate to an overloaded cell in acall connection.

FIG. 1 is a diagram illustrating a mobile communication system to whichthe present disclosure is applied. A mobile communication system 100illustrated in FIG. 1 is a 3GPP LTE system; however, a mobilecommunication system of the present disclosure is not limited to the3GPP LTE system.

Referring to FIG. 1, the mobile communication system 100 may besimplified to have a 2-node structure of a plurality of eNBs 103 and aplurality of eGGSNs (enhanced Gateway GPRS (General Packet RadioService) Support Nodes) 105.

A UE 101 may connect to an Internet protocol network 130 by an E-RAN(Enhanced-Radio Access Network) 110. The eNBs 103 are connected to theUE 101 through radio channels. One eNB 103 includes a plurality ofcells, and the UE 101 may connect to at least two cells of the eNB 103.

The UE 101 repeats an operation for waking up at a fixed time,monitoring a predetermined channel for a predetermined period, and thenshifting to a sleep mode. At this time, when an appropriate cell isfound in an idle mode, the UE 101 performs a cell selection/reselectionprocess. That is, the UE 101 performs an appropriate cellselection/reselection process in order to acquire downlinksynchronization in the idle mode and receive system information and thelike of a corresponding cell. However, in a multi-carrier environment,since a plurality of carriers exist, a carrier selection process shouldbe included in the cell selection/reselection process.

In a conventional mobile communication system, such cellselection/reselection has been performed for an appropriate cell by theUE 101 regardless of a current load state of a carrier. Also in amulti-carrier based mobile communication system, in the case of carrierselection, a load adjustment algorithm has not been applied to a cellselection process of the UE 101. Therefore, in a UE connection, aconnection attempt to an overloaded cell has not been controlled.

Embodiments of the present disclosure are for providing the UE 101 witha search rate and cell reselection priority by a carrier on the basis ofinformation representing load on each carrier that is used in a mobilecommunication system in which the eNB 103 distributes a UE, and indetail, the eNB 103 determines cell reselection priority and a searchrate for each carrier according to embodiments (predeterminedconditions) of the present disclosure, and transmits informationrepresenting the cell reselection priority to the UE 101. The searchrate, for example, has a low value as the load (the congestion state) ofa carrier available in at least one cell is large. Accordingly, acarrier with low load (that is, a carrier with relatively highavailability) has a high search rate, and a carrier with relativelylarge load has a low search rate.

Then, the UE 101 receives the information representing the cellreselection priority for each carrier, and selects a carrier with thehighest priority as a cell reselection target carrier. The informationrepresenting load for each carrier includes at least one of informationrepresenting carrier distribution and information representingdistribution of active UEs, wherein the information representing carrierdistribution indicates distribution of the number of eNBs (or cells)using the same frequency band among Enbs managed by an RAN EMS (ElementManagement System), and the information representing distribution ofactive UEs indicates distribution of the number of active UEs by eachfrequency band being operated in one eNB.

To this end, a method and a device, in which the eNB 103 of amulti-carrier based mobile communication system according to theembodiments of the present disclosure distributes the UE 101 for eachcarrier, will be described in detail.

Firstly, a method, in which the eNB 103 transmits informationrepresenting cell reselection priority for each carrier to the UE 101 inorder to distribute the UE 101 for each carrier in the embodiments ofthe present disclosure, is as follows.

In a first embodiment of the present disclosure, an operator sets cellreselection priority and a search rate that are fixed by a carrier. Thatis, the eNB 103 according to the first embodiment of the presentdisclosure receives the cell reselection priority and the search rate,which are fixed by a carrier, from the operator, and transmitsinformation representing the received cell reselection priority fixed bya carrier to the UE 101.

In second and third embodiments of the present disclosure, the cellreselection priority and the search rate are determined on the basis ofcarrier distribution. That is, the eNB 103 according to the secondembodiment of the present disclosure receives the cell reselectionpriority fixed by a carrier from the operator, determines the searchrate by a carrier on the basis of the carrier distribution, andtransmits information representing the received cell reselectionpriority fixed by a carrier to the UE 101. Furthermore, the eNB 103according to the third embodiment determines the cell reselectionpriority and the search rate by a carrier on the basis of the carrierdistribution, and transmits information representing the determined cellreselection priority to the UE 101.

In fourth and fifth embodiments of the present disclosure, the cellreselection priority and the search rate are dynamically determined onthe basis of distribution of active UEs by a carrier. The active UEindicates a UE in an active state. That is, the eNB 103 according to thefourth embodiment of the present disclosure receives the cellreselection priority fixed by a carrier from the operator, determinesthe search rate by a carrier on the basis of the distribution of theactive UEs, and transmits information representing the received cellreselection priority fixed by a carrier to the UE 101. Furthermore, theeNB 103 according to the fifth embodiment of the present disclosuredetermines the cell reselection priority and the search rate by acarrier on the basis of the distribution of the active UEs, andtransmits information representing the determined cell reselectionpriority to the UE 101.

Furthermore, in a sixth embodiment of the present disclosure, the cellreselection priority and the search rate are dynamically determined onthe basis of cell load average information by a carrier. That is, theeNB 103 according to the sixth embodiment of the present disclosuredetermines the cell reselection priority and the search rate on thebasis of the cell load average information by a carrier, and transmitsinformation representing the determined cell reselection priority to theUE 101. The operation of the eNB 103, for example, may also be operatedin a SON (Self Optimizing Network) server.

In another embodiment of the aforementioned first to sixth embodiments,the eNB 103 may determine a search rate by a carrier on the basis ofinformation representing load for a carrier such as carrierdistribution, distribution of active UEs, distribution of the number ofeNBs using the same frequency band, or a cell load average, determinecell reselection priority for a corresponding idle UE on the basis ofthe determined search rate, and then transmit the determined cellreselection priority to the idle UE.

Hereinafter, the first to sixth embodiments of the present disclosurewill be described in detail with reference to the accompanying tablesand drawings.

The eNB 103 according to the first embodiment of the present disclosurereceives the cell reselection priority and the search rate, which arefixed by a carrier, from the operator. A method, in which the operatordetermines the cell reselection priority and the search rate, which arefixed by a carrier, may be shown in Table 1 below as one example.

TABLE 1 Carrier Cell (ARFCN) Cell Search reselection (system reselectionrate probability per Bandclass parameter) priority (optional) carrier(optional) 1.9 GHz Aaaa 7 6 6/10 800M Bbbb 5 3 3/10 ZZ frq#1 Cccc 3 11/10

In Table 1 above, the “Carrier (ARFCN: Absolute Radio Frequency ChannelNumber)” indicates an identifier of a carrier. The cell reselectionpriority, for example, has values of 0 to 7 in an LTE system, and apriority is high as the cell reselection priority has a high value.

The eNB 103 transmits the cell reselection priority fixed by a carrierand received from the operator to the UE 101 through a systeminformation block (SIB) or an RRC connection release message. The eNBassigns a cell reselection priority value to a UE on the basis of asearch rate by a carrier in which an RRC connection is released. InTable 1 above, the cell reselection probability per carrier indicates aratio by which the cell reselection priority value is assigned to eachUE on the basis of the search rate by a carrier.

In another embodiment of the present disclosure, the eNB 103 candetermine again cell reselection priority, which is to be transmitted toa corresponding UE, on the basis of the search rate. For example, inTable 1 above, for RRC connection release target UE of 30%(corresponding to the search rate of “3”), cell reselection priority ofa carrier Bbbb, for example, is set to “7” from “5” again and cellreselection priority of a carrier Aaaa, for example, is set to a valuelower than “7” again. Then, information representing the cellreselection priority determined (set) again in the aforementioned schemeis transmitted to the corresponding UE. In the case of the aboveexample, the identifier (Carrier (ARFCN)) of the corresponding carrierBbbb and the value of “7” that is the cell reselection prioritydetermined again, the identifier of the carrier Aaaa and a value lowerthan “6” that is the cell reselection priority determined again, anidentifier of a carrier Cccc and a value lower than “6” that is the cellreselection priority determined again are provided to the RRC connectionrelease target UE of 30% (corresponding to the search rate of “3”) asinformation representing the cell reselection priority. A scheme ofdetermining the aforementioned cell reselection priority again may alsobe applied to the following second to sixth embodiments in the samemanner.

FIG. 2 is a flowchart illustrating a method for distributing an idle UEby a carrier in the mobile communication system according to the secondembodiment of the present disclosure.

Referring to FIG. 2, in step 5201, an LTE system manager (LSM) 107selects a scheme of determining cell reselection priority and a searchrate. An operator of the LSM 107 determines cell reselection priority bya carrier according to the second embodiment of the present disclosureamong the embodiments of the present disclosure, and selects a scheme inwhich the eNB 103 determines a search rate on the basis of carrierdistribution. In step S203, the LSM 107 transmits the cell reselectionpriority fixed by a carrier and determined by the operator and theselected scheme to the eNB 103.

In step S205, the eNB 103 receives the cell reselection priority fixedby a carrier and the selected scheme from the LSM 107, monitors carrierdistribution according to the selected scheme, and determines the searchrate by a carrier on the basis of the monitored carrier distribution. Ascheme, in which the eNB 103 determines the search rate by a carrier onthe basis of the carrier distribution, may be shown in Table 2 below asone example.

TABLE 2 Cell Carrier reselction Cell (ARFCN) priority reselction (system(operator Carrier Search probability Bandclass parameter) setting value)distribution rate per carrier 1.9 GHz Aaaa 7 0.7 7 7/10 800M Bbbb 5 0.22 2/10 ZZ frq#1 Cccc 3 0.1 1 1/10

In Table 2 above, the carrier distribution may be determined usingEquation 1 below, the search rate by a carrier may be determined usingEquation 2 below, and the cell reselection probability per carrier maybe determined using Equation 3 below.

$\begin{matrix}{d_{i} = \frac{C_{i}}{c}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In Equation 1 above, di indicates carrier distribution, Ci indicates thenumber of carriers i in an eNB, and c indicates the maximum number ofcarriers in the eNB.

$\begin{matrix}{S_{i} = {d_{i}*10}} & {{Equation}\mspace{14mu} 2} \\{P_{i} = \frac{S_{i}}{\sum\limits_{i = 1}^{k}S_{i}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

In Equation 3 above, si indicates a search rate of a carrier i, and kindicates the total number of carriers of a multi-carrier mobilecommunication network. In step S207, the eNB 103 determines whether thecell reselection priority fixed by a carrier is allowed to be includedin an RRC connection release message. When the cell reselection priorityfixed by a carrier is allowed to be included in the RRC connectionrelease message, the eNB 103 transmits the RRC connection releasemessage including the cell reselection priority fixed by a carrier tothe UE 101 in step S209. When a preset timer is expired, the UE 101deletes the reselection priority received through the RRC connectionrelease message in step S211. When the cell reselection priority fixedby a carrier is not allowed to be included in the RRC connection releasemessage, the eNB 103 transmits the cell reselection priority fixed by acarrier to the UE 101 through a system information block (SIB) in stepS213. The SIB may be SIB5.

FIG. 3 is a flowchart illustrating a method for distributing an idle UEby a carrier in the mobile communication system according to the thirdembodiment of the present disclosure.

Referring to FIG. 3, in step S301, the LSM 107 selects a scheme ofdetermining the cell reselection priority and the search rate. The LSM107 selects a scheme in which the eNB 103 determines the cellreselection priority and the search rate by a carrier on the basis ofcarrier distribution according to the third embodiment of the presentdisclosure among the embodiments of the present disclosure. In stepS303, the LSM 107 transmits the selected scheme to the eNB 103 such thatthe eNB 103 operates according to the third embodiment of the presentdisclosure.

Then, in step S305, the eNB 103 monitors carrier distribution, anddetermines the cell reselection priority and the search rate by acarrier the basis of the monitored carrier distribution. A scheme, inwhich the eNB 103 determines the cell reselection priority and thesearch rate by a carrier on the basis of the carrier distribution, maybe shown in Table 3 below as one example.

TABLE 3 Carrier Cell (ARFCN) Cell reselection (system Carrierreselection Search probability Bandclass parameter) distributionpriority rate per carrier 1.9 GHz Aaaa 0.7 7 7 7/10 800M Bbbb 0.2 6 22/10 ZZ frq#1 Cccc 0.1 5 1 1/10

In Table 3 above, the carrier distribution, the search rate by acarrier, and the cell reselection probability per carrier are determinedusing Equation 1, Equation 2, and Equation 3 above. Furthermore, whenthe search rate of the carrier i has the largest value, sinceavailability is large, the cell reselection priority by a carrier isassigned in sequence of {7, 6, 5, 4, 3, 2, 1}.

In step S307, the eNB 103 determines whether the determined cellreselection priority by a carrier is allowed to be included in the RRCconnection release message. When the determined cell reselectionpriority by a carrier is allowed to be included in the RRC connectionrelease message, the eNB 103 transmits the determined cell reselectionpriority by a carrier to the UE 101 through the RRC connection releasemessage in step S309. When a preset timer is expired, the UE 101 deletesthe reselection priority received through the RRC connection releasemessage in step S311. When the determined cell reselection priority by acarrier is not allowed to be included in the RRC connection releasemessage, the eNB 103 transmits the determined cell reselection priorityby a carrier to the UE 101 through the SIB in step S313.

FIG. 4 is a flowchart illustrating a method for distributing an idle UEby a carrier in the mobile communication system according to the fourthembodiment of the present disclosure.

Referring to FIG. 4, in step S401, the LSM 107 selects a scheme ofdetermining the cell reselection priority and the search rate. Anoperator of the LSM 107 determines the cell reselection priority fixedby a carrier according to the fourth embodiment of the presentdisclosure among the embodiments of the present disclosure, and selectsa scheme in which the eNB 103 determines the search rate by a carrier onthe basis of active UE distribution. In step S403, the LSM 107 transmitsthe cell reselection priority fixed by a carrier and determined by theoperator and the selected scheme to the eNB 103.

In step S405, the eNB 103 receives the cell reselection priority fixedby a carrier and the selected scheme from the LSM 107, and determinesthe search rate by a carrier on the basis of the active UE. A scheme, inwhich the eNB 103 determines the search rate by a carrier on the basisof the carrier distribution, may be shown in Table 4 below as oneexample.

TABLE 4 Active UE Cell Carrier Load rate reselection (ARFCN) Cell(Active probability (system reselection UE/Maximum Search per Bandclassparameter) priority UE/carrier) rate carrier 1.9 GHz Aaaa 7 0.4 6 6/10800M Bbbb 5 0.7 3 3/10 ZZ frq#1 Cccc 3 0.9 1 1/10

In Table 4 above, the carrier distribution may be determined usingEquation 4 below, the search rate by a carrier may be determined usingEquation 5 below, and the cell reselection probability per carrier maybe determined using Equation 6 below.

$\begin{matrix}{r_{i} = \frac{N_{i}}{M_{i}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

In Equation 4 above, ri indicates carrier distribution, Ni indicates thenumber of active UEs in the carrier i, and Mi indicates the permissiblemaximum number of UEs in the carrier i.

$\begin{matrix}{S_{i} = {\left( {1 - r_{i}} \right)*10}} & {{Equation}\mspace{14mu} 5} \\{P_{i} = \frac{S_{i}}{\sum\limits_{i = 1}^{k}S_{i}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

Then, in step S407, the eNB 103 determines whether the cell reselectionpriority fixed by a carrier is allowed to be included in the RRCconnection release message. When the cell reselection priority fixed bya carrier is allowed to be included in the RRC connection releasemessage, the eNB 103 transmits the cell reselection priority fixed by acarrier to the UE 101 through the RRC connection release message in stepS409. When a preset timer is expired, the UE 101 deletes the reselectionpriority received through the RRC connection release message in stepS411. When the cell reselection priority fixed by a carrier is notallowed to be included in the RRC connection release message, the eNB103 transmits the cell reselection priority fixed by a carrier to the UE101 through the SIB in step S413.

FIG. 5 is a flowchart illustrating a method for distributing an idle UEby a carrier in the mobile communication system according to the fifthembodiment of the present disclosure.

Referring to FIG. 5, in step S501, the LSM 107 selects a scheme ofdetermining the cell reselection priority and the search rate. The LSM107 selects a scheme in which the eNB 103 determines the cellreselection priority and the search rate by a carrier on the basis of anactive UE according to the fifth embodiment of the present disclosureamong the embodiments of the present disclosure. In step S503, the LSM107 transmits the selected scheme to the eNB 103 such that the eNB 103operates according to the fifth embodiment of the present disclosure.

Then, in step S505, the eNB 103 determines the cell reselection priorityand the search rate by a carrier on the basis of the active UE. Ascheme, in which the eNB 103 determines the cell reselection priorityand the search rate by a carrier on the basis of the carrierdistribution, may be shown in Table 5 below as one example.

TABLE 5 Active UE Carrier Load rate Cell (ARFCN) (Active Cellreselection (system UE/Maximum reselection Search probability Bandclassparameter) UE/carrier) priority rate per carrier 1.9 GHz Aaaa 0.4 7 66/10 800M Bbbb 0.7 6 3 3/10 ZZ frq#1 Cccc 0.9 5 1 1/10

In Table 5 above, the carrier distribution, the search rate by acarrier, and the cell reselection probability per carrier are determinedusing Equation 4, Equation 5, and Equation 6 above. Furthermore, whenthe search rate of the carrier i has the largest value, sinceavailability is large, the cell reselection priority by a carrier isassigned in sequence of {7, 6, 5, 4, 3, 2, 1}.

In step S507, the eNB 103 determines whether the determined cellreselection priority by a carrier is allowed to be included in the RRCconnection release message. When the determined cell reselectionpriority by a carrier is allowed to be included in the RRC connectionrelease message, the eNB 103 transmits the determined cell reselectionpriority by a carrier to the UE 101 through the RRC connection releasemessage in step S509. When a preset timer is expired, the UE 101 deletesthe reselection priority received through the RRC connection releasemessage in step S511. When the determined cell reselection priority by acarrier is not allowed to be included in the RRC connection releasemessage, the eNB 103 transmits the determined cell reselection priorityby a carrier to the UE 101 through the SIB in step S513.

FIG. 8 is a flowchart illustrating a method for distributing an idle UEby a carrier in the mobile communication system according to the sixthembodiment of the present disclosure.

Referring to FIG. 8, in step S801, the LSM 107 selects a scheme ofdetermining the cell reselection priority and the search rate. The LSM107 selects a scheme in which the eNB 103 determines the cellreselection priority and the search rate by a carrier on the basis ofcell load average information by a carrier according to the sixthembodiment of the present disclosure among the embodiments of thepresent disclosure. In step S803, the LSM 107 transmits the selectedscheme to the eNB 103 such that the eNB 103 operates according to thesixth embodiment of the present disclosure.

In step S805, the eNB 103 determines the cell reselection priority andthe search rate by a carrier on the basis of the cell load averageinformation by a carrier. A scheme, in which the eNB 103 determines thesearch rate by a carrier on the basis of the cell load averageinformation by a carrier, may be shown in Table 6 below as one example.

TABLE 6 Cell load Cell reselection Carrier average by probability perBand Class (ARFCN) carrier Search rate carrier 1.9 GHz Aaaa 70% 3 3/8800M Bbbb 50% 5 5/8

In Table 6 above, the cell load average by a carrier is determined onthe basis of cell load information of a serving cell and a neighbor cellderived by percentage. In a carrier of the serving cell, n−1 neighborcells with high priority are selected from among the serving cell andneighbor cells of the corresponding carrier managed by the serving cell,and a cell load average of the n cells including the serving cell iscalculated. In a carrier different from the carrier of the serving cell,n neighbor cells with high priority are selected from among the neighborcells of the corresponding carrier managed by the serving cell, and acell load average is calculated. An operator can set n that is aparameter, which is used when the cell load average by a carrier iscalculated, through the LSM.

In Table 6 above, the search rate by a carrier may be determined usingEquation 7 below.

$\begin{matrix}{S_{i} = {{round}\left\{ {\left( {1 - \frac{g_{i}}{100}} \right) \times 10} \right\}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

In Equation 7 above, gi indicates a cell load average of the carrier i,which is expressed by percentage, and round { } indicates a round-offfunction.

FIG. 6 is a block diagram schematically illustrating a configuration ofthe eNB 103 according to the embodiment of the present disclosure.

Referring to FIG. 6, the eNB 103 includes a reception unit 601, acontrol unit 603, and a transmission unit 605.

The reception unit 601 receives the scheme of determining the cellreselection priority and the search rate from the LSM 107. The receptionunit 601 receives at least one of the cell reselection priority and thesearch rate from the operator according to the aforementionedembodiments of the present disclosure. Furthermore, the reception unit601 receives cell load information on neighbor cells included in acorresponding eNB from a neighbor eNB.

The control unit 603 controls the operations of the reception unit 601and transmission unit 603, and determines at least one of the cellreselection priority and the search rate on the basis of the carrierdistribution or the distribution of active UEs according to the receivedscheme of determining the cell reselection priority and the search rate(that is, according to the aforementioned embodiments of the presentdisclosure).

The transmission unit 605 transmits the cell reselection priority to theUE 101.

FIG. 6 illustrates the case in which the reception unit 601 and thetransmission unit 605 are provided in the form of separate units, but itis of course that the reception unit 601 and the transmission unit 605may be provided in the form of a single unit.

Hereinafter, the operation of each unit included in the eNB 103 will bedescribed in detail with reference to FIG. 7.

FIG. 7 is a flowchart illustrating a method in which the eNB 103according to an embodiment of the present disclosure distributes an idleUE.

Referring to FIG. 7, in step S701, the reception unit 601 receives ascheme of determining the cell reselection priority and the search ratefrom the LSM 107. Step S703, step S705, step S711, step S715, or stepS721 is performed according to the scheme of determining the cellreselection priority and the search rate.

That is, according to the first embodiment of the present disclosure, instep S703, the reception unit 601 receives the cell reselection priorityand the search rate fixed by a carrier from the operator. In step S725,the transmission unit 605 transmits the received cell reselectionpriority fixed by a carrier to the UE 101. The operations of thereception unit 601 and the transmission unit 605 are controlled by thecontrol unit 603.

According to the second embodiment of the present disclosure, in stepS705, the reception unit 601 receives the cell reselection priorityfixed by a carrier from the operator. The control unit 707 monitors thecarrier distribution through the reception unit 601 in step S707 anddetermines the search rate on the basis of the monitored carrierdistribution in step S709. In step S725, the transmission unit 605transmits the received cell reselection priority fixed by a carrier tothe UE 101.

According to the third embodiment of the present disclosure, the controlunit 707 monitors the carrier distribution through the reception unit601 in step S711 and determines the cell reselection priority and thesearch rate by a carrier on the basis of the monitored carrierdistribution in step S713. In step S725, the transmission unit 605transmits the determined cell reselection priority by a carrier to theUE 101.

According to the fourth embodiment of the present disclosure, in stepS715, the reception unit 601 receives the cell reselection priorityfixed by a carrier. The control unit 707 monitors the distribution ofactive UEs through the reception unit 601 in step S717 and determinesthe search rate on the basis of the monitored distribution of active UEsin step S719. In step S725, the transmission unit 605 transmits thereceived cell reselection priority fixed by a carrier to the UE 101.

According to the fifth embodiment of the present disclosure, the controlunit 603 monitors the distribution of active UEs through the receptionunit 601 in step S721 and determines the cell reselection priority andthe search rate by a carrier on the basis of the monitored distributionof active UEs in step S723. In step S725, the transmission unit 605transmits the determined cell reselection priority by a carrier to theUE 101.

According to the sixth embodiment of the present disclosure, the controlunit 603 monitors a cell load average through the reception unit 601 instep S727 and determines the cell reselection priority and the searchrate by a carrier on the basis of the monitored cell load average by acarrier in step S729. In step S725, the transmission unit 605 transmitsthe determined cell reselection priority by a carrier to the UE 101.

Although the embodiment has been described in the detailed descriptionof the present disclosure, the present disclosure may be modified invarious forms without departing from the scope of the presentdisclosure. Thus, the scope of the present disclosure shall not bedetermined merely based on the described exemplary embodiments andrather determined based on the accompanying claims and the equivalentsthereto.

What is claimed is:
 1. A base station for supporting cell reselection ofa user equipment (UE) by a base station in a mobile communication systemusing a plurality of carriers, the base station comprising: atransmitter; and a controller configured to: obtain load information ofeach carrier among the plurality of carriers; assign a cell reselectionpriority of the each carrier based on the obtained load information, thecell reselection priority being one integer among 0 to 7; and transmit,to the UE, via the transmitter, information indicating the assigned cellreselection priority of the each carrier.
 2. The base station of claim1, wherein the load information includes information on carrierdistribution and information on distribution of active UEs, and whereinthe information on the carrier distribution represents a distribution ofcells using a same frequency band, and the information on thedistribution of the active UEs represents a distribution of a number ofthe active UEs using a same carrier for each frequency band.
 3. The basestation of claim 1, wherein the load information of each carrier isobtained based on a number of UEs using the each carrier, and whereinthe cell reselection priority is used in case that the UE is in an idlemode.
 4. The base station of claim 1, wherein the controller is furtherconfigured to: determine a relative availability of the each carrierbased on the obtained load information on the each carrier, and assignthe cell reselection priority of the each carrier based on thedetermined relative availability of the each carrier.
 5. The basestation of claim 1, wherein the controller is configured to: transmit,to the UE, via the transmitter, the information indicating the assignedcell reselection priority of the each carrier through a systeminformation block (SIB).
 6. The base station of claim 2, wherein thedistribution of the active UEs is obtained by a ratio of the number ofthe active UEs in each carrier to a permissible maximum number of UEs ineach carrier.
 7. The base station of claim 2, wherein the carrierdistribution is obtained by a ratio of a number of carriers using thesame frequency band to a maximum number of carriers in the base station.8. A method for supporting cell reselection of a user equipment (UE) bya base station in a mobile communication system using a plurality ofcarriers, the method comprising: obtaining load information of eachcarrier among the plurality of carriers; assigning a cell reselectionpriority of the each carrier based on the obtained load information, thecell reselection priority being one integer among 0 to 7; andtransmitting, to the UE, information indicating the assigned cellreselection priority of the each carrier.
 9. The method of claim 8,wherein the load information includes information on carrierdistribution and information on distribution of active UEs, and whereinthe information on the carrier distribution represents a distribution ofcells using a same frequency band, and the information on thedistribution of the active UEs represents a distribution of a number ofthe active UEs using a same carrier for each frequency band.
 10. Themethod of claim 8, wherein the load information of each carrier isobtained based on a number of UEs using the each carrier, and whereinthe cell reselection priority being used in case that the UE is in anidle mode.
 11. The method of claim 8, further comprising: determining arelative availability of the each carrier based on the obtained loadinformation on the each carrier, and assigning the cell reselectionpriority of the each carrier based on the determined relativeavailability of the each carrier.
 12. The method of claim 8, whereintransmitting, to the UE, information comprising: transmitting, to theUE, the information indicating the assigned cell reselection priority ofthe each carrier through a system information block (SIB).
 13. Themethod of claim 9, wherein the distribution of the active UEs isobtained by a ratio of the number of the active UEs in each carrier to apermissible maximum number of UEs in each carrier.
 14. The method ofclaim 9, wherein the carrier distribution is obtained by a ratio of anumber of carriers using the same frequency band to a maximum number ofcarriers in the base station.